In yet another installment of my series examining the supposed health detriments of eating meat we move to the topic of high blood pressure. I’ve heard people claim that meat gives you high blood pressure (usually citing some epidemiological studies on vegetarians with low blood pressure to support it). Since high blood pressure is associated with and appears to play a role in cardiovascular disease, including stroke (1) this would be bad for the meat eaters. Well, let’s give a quick run through of some controlled trials to see how true this theory is.
Part I: Is the Fat Bad for Blood Pressure?
The fat contained in meat is primarily monounsaturated (MUFA) and saturated (SFA), rather than polyunsaturated (PUFA). Replacing saturated fat with polyunsaturated fat in one study had no effect on blood pressure (2). In another study, replacing saturated fat with monounsaturated fat caused a small lowering of blood pressure, but only when fat intake was low (3). In a 1981 study from researchers in the Netherlands, several manipulations of the ratio of polyunsaturated to other fats (MUFA and SFA) in the diet failed to produce any significant effect on blood pressure (4). Another study which manipulated the polyunsaturated to saturated fat ratio of the diet in school children reported no apparent effect on blood pressure (5). A 17 day trial reported that the effects of linoleic acid (a PUFA) compared to oleic acid (a MUFA) on blood pressure were not different (6). Thus, it appears that different types of fat have little if any noticeable effect on blood pressure compared to each other.
One study on diabetics found that consuming monounsaturated fat, the primary fat in most meats, led to lower blood pressure than consuming carbohydrates (7). However, the method used in this study to measure blood pressure has been criticized and a similar study on diabetics found no difference between a high monounsaturated and high carbohydrate diets (9). Another study comparing monounsaturated fat to carbohydrates in healthy volunteers noted no difference on blood pressure (8). Finally, a meta analysis of 10 studies comparing high MUFA to high carbohydrate diets found that monounsaturated fat led to insignificantly lower blood pressure levels (10).
In a cross over study of 21 subjects testing the effects of saturated fat, polyunsaturated fat, and carbohydrates on several markers of health, no differential effects were seen between any of the three diet periods (19).
To conclude this section on fats and blood pressure, let’s look at the findings of a meta analysis of numerous diet trials which concluded “exchanging saturated, monounsaturated, and polyunsaturated fatty acids, and changing the content of total dietary fat and carbohydrates all had no substantial effect on BP” (27).
Part II: The Effect of Eating (or Not Eating) Meat on Blood Pressure
Several studies on diet and blood pressure have been conducted in which meat protein was compared to other sources of protein. In two separate studies the effects of protein from meat was compared to vegetarian sources of protein (i.e. vegetables, eggs, dairy products, etc.). At the end of both trials the same effects on blood pressure were seen between both protein groups (11,12). Four other studies compared meat protein to protein of vegetable origin and also found no differential effects on blood pressure (13,14,15,16).
Another study compared the effects of replacing carbohydrates with 250 grams of lean red meat in 60 hypertensive individuals, concluding that eating lean red meat led to lower systolic blood pressure (17). Another study fed 250 grams of beef to the diet of 21 “strict” vegetarians, this time finding that systolic blood pressure increased (24). It seems not entirely unreasonable to speculate that perhaps the stress felt by these strict vegetarians adding a large amount of beef to their diet may have responsible for their increased blood pressure.
The well known clinical trial on the DASH diet (Dietary Approach to Stop Hypertension) is oft cited when discussing diet and blood pressure (19). The study used 3 different diets and 459 subjects, so it was a powerful study. It’s sometimes cited as evidence of the negative role of meat on blood pressure, due to the fact the DASH group replaced a serving of meat primarily with low fat dairy products and vegetables and saw a greater reduction in blood pressure. So does this show eating low fat dairy products is better for blood pressure? Not really, since the low fat dairy products increased the total protein content of the DASH group’s diet. This is important because it has been seen in several studies that increased protein (largely from dairy) in the diet may improve blood pressure compared to increasing fat (20). If meat had contributed to an equal protein intake we would be more able to infer that meat protein is less beneficial than protein from diary products. Furthermore, the increased calcium intake may also have been responsible for the lower blood pressure levels in the DASH group, an effect which long term studies suggest may be transient (21).
Moving on, we now have a study which lasted two years that compared two different diets; one low in carbohydrates and featuring a fair amount of meat, the other low in fat and containing much less meat. At the end of the trial the higher meat eating group had lower systolic blood pressure (22). A trial with the same general structure (low carb, higher meat diet vs. low fat diet) found no difference in blood pressure between the groups (23). Finally, a meta analysis of five long term diet trials comparing low fat to low carbohydrate diets (the latter containing more meat than the former) found no difference in blood pressure between the two different diets (28).
A study on 18 healthy men had them eat walnuts in place of “fatty foods, meat, and visible fat” for 61 days (25). At the end of the trial no effects on blood pressure were seen.
Finally, let’s look at an interesting study which had 19 men and women eliminate all meat, eggs, and dairy fat from their diet 3 months (26). The result? None, really. No effect of such a dietary change on blood pressure was not seen.
While no notable trend (or perhaps a trend towards no effect) emerging from this overview, these studies cast serious doubt on the idea that eating meat will lead to high blood pressure. There are almost certainly many more significant factors at play between a person’s diet and blood pressure than whether or not they eat meat. For people with hypertension it would seem the recommendation to avoid meat is a distraction from actual methods of treating their illness.